1. Field
The present disclosure generally relates to processes for manufacturing and/or repairing composite structures, and deals more particularly with monitoring composite structures as they are being cured.
2. Background
Fiber reinforced thermoset resin structures, such as carbon fiber epoxy, may be cured through the application of heat and pressure using autoclave or out-of-autoclave processes. In order to optimize properties of the cured structure, it is sometimes desirable to monitor temperature and/or pressure during curing to determine whether either of these process parameters are outside of specified ranges.
Several techniques have been employed to monitor temperature and/or pressure during the cure process, however each has disadvantages. For example, thermocouples may be located at specific locations on a composite structure or a composite repair in order to monitor temperature, however thermocouples only provide temperature information at specific locations and may not reveal out-of-range temperature information at other locations. Thermocouples may have less than desired reliability, and may not be practical for use on large, complex structures or composite repairs that extend over a relatively large area. In some applications, thermocouples may also interfere with the cure process itself, particularly where thermocouples are placed in incorrect areas beneath vacuum bagging material.
IR (infrared) cameras may be used to monitor temperature within exposed areas of a composite structure during curing, however infrared cameras are relatively expensive, are limited to line-of-sight monitoring, and are not capable of monitoring areas of a structure beneath the vacuum bags.
Techniques have been devised to measure the pressure being applied to a composite structure or composite repair during curing using discrete pressure sensors. However, the sensed pressure information is limited to the location of the pressure sensors, consequently, this technique does not provide useful information concerning pressure over large areas of the structure. Moreover, the use of pressure sensors can, themselves result in undesirable mark-off when installed in highly convex or concave regions of a structure where pressure measurements may be particularly useful. Furthermore, it may be impractical to use pressure sensors with certain types of curing equipment, such as press claves.
Accordingly, there is a need for a method and apparatus for monitoring process parameters, such as temperature and pressure, over large areas of a composite structure during curing. There is also a need for a method and apparatus as described above which provide a permanent visual map of temperature and pressure over the entire area of a composite structure during curing, and which may be employed to alter process parameters in real-time during the curing process, thereby optimizing the properties of the cured composite structure or repair.